Montana Public Radio

Bug Bytes: Aphid Ranchers

Jul 1, 2019

If you’ve ever noticed a group of ants milling about on a leaf or the stem of a plant and wondered why, take a closer look. You might only be seeing half of what’s going on.

While they lack pickup trucks, fencing pliers, and other tools of the trade of their human counterparts, these ants are likely ranchers. But instead of cows, they’re carefully tending their herd of aphids.

Aphids are small insects that feed on the sap of plants. But unlike an unappetizing cow pie, aphids excrete a sugary substance called honeydew that ants love to eat.

Ants tending to their aphid herd.
Credit Missoula Insectarium

Some species of ants simply follow their aphids, waiting to devour the droppings. But others take a more active role in obtaining the fruits of their labor by “milking” their herds by tickling them with their antennae.

But what do the aphids get out of the relationship?

Like any good rancher, the ants want to provide for and protect their livestock. Ants will shepherd their aphid flocks to better sources of food, sometimes carrying them from one plant to another. Ants will aggressively defend their herd from predators, attacking ladybugs and other insects that like to prey on aphids. And to ensure the future of the herd, ants will care for and protect the aphids’ eggs, even keeping them warm and safe inside the ant colony during winter.

To ensure their herd doesn’t wander off, ants have been known to remove their aphids’ wings. They’ve even developed chemicals on their feet that tranquilize the aphids, making them easier to wrangle.

While humans might have more sophisticated livestock equipment, ants have been herding aphids for 50 million years. So the next time you notice a group on ants on a plant, take a close look. Chances are you’ll find dozens of tiny livestock being carefully tended.

Bug Bytes is made possible by the Missoula Butterfly House and Insectarium, and Montana Public Radio. This show is also supported by funding from the Greater Montana Foundation: Encouraging communication on issues, trends and values of importance to Montanans.